The phenomena of intermodulation appear for electromagnetic devices operating at several frequencies simultaneously when objects behaving in non-linear manner are located close by. Intermodulation is the result of distortions generated by these non-linear objects from an incident electromagnetic wave. Intermodulation manifests itself especially through the appearance of new components of frequencies in the electromagnetic wave. The frequencies of these intermodulation components are obtained by addition or subtraction of multiples of the frequencies that are present in the electromagnetic wave incident on said non-linear object. The result of the addition of the moduli of the multiplying factors of the frequencies of the incident electromagnetic wave that are used to obtain the frequency of an intermodulation component is designated by “order of intermodulation”.
Generally it is sought to evaluate the power of distortions of passive intermodulation, because they cannot all be eliminated by filtering—unlike distortions of out-of-band active intermodulation (caused by active components). Now, the power of the passive intermodulation products becomes significant in electronic devices operating at high power levels.
It is therefore particularly important to determine the power of intermodulation products produced by non-linear objects situated in proximity to electromagnetic devices such as transmitting/receiving antennas, for example.
In fact, in electronic devices of broadband telecommunications, products of passive intermodulation that are derived from the transmission signals have frequencies in the reception band. This is the case all the more so, since the bands of radio frequencies for telecommunications are more and more densely occupied. Now, since the reception signals are always of lower power than the transmission signals, the products of passive intermodulation that are derived from the transmission signals may significantly add noise to the reception of information signals.
This is the case, for example, in devices for transmission/reception of long-range telecommunications signals that use a large number of carrier frequencies for transmission and for reception, and in broadband. This phenomenon is particularly inconvenient in telecommunications devices on board satellites, on board aircraft or, on the ground, in telecommunications relays for mobile phones. The phenomena of intermodulation are sufficiently important in this case to have led some manufacturers of satellites to duplicate their transmission/reception device, which represents a very high additional cost of manufacture and launch.
It is therefore essential to be able to evaluate and predict the power levels of these intermodulation products, in order to take them better into account when designing the device. It is, in particular, essential to be able to measure the powers produced by an object in particular, especially by a sample of particular material.
In numerous processes for measuring intermodulation products produced by an object an electromagnetic wave is emitted by two antennas onto a reflector, and the wave reflected by said object is measured by a receiver. Such a process is accordingly described in U.S. Pat. No. 6,144,692. The receiver includes a demodulation device including a demultiplexer enabling a power measurement to be carried out of each component of the electromagnetic wave received by the receiver.
Such devices present numerous drawbacks. Accordingly, such a device does not enable measurements to be carried out in certain important frequency bands. Accordingly, it is not possible to carry out measurements at frequencies situated between those of two fundamental components forming an incident wave, nor at frequencies situated beyond the total pass-band of the demultiplexer. It is also impossible to measure powers of intermodulation products, the frequency of which is outside the reception band of the demultiplexer.
In addition, such demultiplexers themselves introduce products of passive intermodulation, and their quality greatly influences the cost of the measuring device.
The invention therefore aims to palliate these drawbacks.
The invention aims to propose a process for measuring intermodulation products enabling a measurement of intermodulation products to be carried out that is reliable and precise for any component of any frequency.
The invention also aims to propose such a process that is economical and simple.